This invention relates to gas testing devices in general and, more particularly, to a new and useful indicator device for the quantitative determination of metal cyanides in aerosol form.
Indicator tubes for the quantitative determination of aerosol-type metal cyanides have not yet been known heretofore. The reason for this lies in the unclear reaction behavior of the aerosols with the indicating preparations of the indicator tubes.
A known method for detecting both volatile and misty arsines uses an indicator tube in which a filter of inorganic or organic silica gel, e.g., glass wadding, cellulose, asbestos, is arranged in front of a highly active silica gel layer. When an air sample is passed therethrough, the arsine mists contained in the sample are retained by the filter and volatile arsines are fixed by the silica gel. Subsequently, a reagent in the form of a solution of tin chloride in concentrated hydrochloric acid is introduced into the indicator tube.
The mist particles retained by the filter are entrained by the reagent and flushed to the silica gel layer. They react with the reagent only on the silica gel. The reaction in the form of an arsenic deposit is always observed in the silica gel layer on the silica gel, regardless of whether arsine mists or volatile compounds are present. The reaction takes place directly between the substances to be detected and the indicating reagent. This measuring method therefore permits only a qualitative determination of the arsines. In addition, the use of the liquid reaction solution is not entirely harmless (see German Patent No. 742,689).
In a known indicator tube for the determination of hydrogen cyanide, mercuric chloride and methyl red are used as a reagent system. However, this reagent system only reacts with hydrogen cyanide, and not with metal cyanides ("Testing Tube Pocketbook", Dr/agerwerk AG, Reprint 2340, May 1976, pp. 82-83).